The present invention generally relates to apparatus and methods for processing scrap tires for reuse, and particularly to apparatus and methods for extracting liquid rubber/fiber/catalyst slurry from the remaining components of the tires, with the liquid slurry and remaining components being in a condition for reuse and/or recycling.
The United States alone scraps about 250,000,000 tires per year or roughly one tire per person per year, with 2-4 billion tires currently stockpiled. These stockpiled tires represent potential threats for both air and water quality plus they provide a breeding ground for mosquitoes. Each of the solutions to the present scrap tire problem has difficulties. One method of disposal is landfilling the tires; however, tires generally do not degrade and whole tires cannot be landfilled because they "bubble up" to the surface. Specific disposal of tires is expensive but does tend to preserve the resource for a later date.
Using scrap tires to develop energy serves two purposes: first, it disposes of the tire, and second, it provides industrial/commercial companies with lower fuel cost energy. The economic cost/benefit of the waste-to-energy (WTE) approach will depend greatly on the particular type of combustor being used. For example, many moving grate type boilers have great difficulty if there is too much steel remaining in the fuel. The cost of removing the steel belts and steel beads from a tire is expensive. Generally speaking, the light belt wire in a typical steel belted radial tire will be consumed in combustors that operate at 870.degree. C. and above. The primary problem is the steel bead. The steel bead survives temperatures in the range of 870.degree.-1370.degree. C. and could present problems in mechanical mechanisms in today's combustors and also provide a problem in the need for removing the steel from the ash. Some boilers have other significant problems in burning tires in the inability to handle the sulfur content and the effect of zinc oxide coating of heat transfer elements.
Recycling of all the tire components is the optimum choice both from the environmental and an economic viewpoint. One of the problems of recycling of scrap tires is the great difficulty in separating the components. The tire companies have spent years making the steel, rubber and fiber virtually non-separable. Pyrolysis has been tried to break a tire into its components but has proven uneconomical because of the lack of a market for the oils and tire char that result. Cryogenics has been used to attempt to separate the components of the tire and in most cases has proven uneconomical. Rubber is a material that is a "thermoset" which means it can be used once and cannot be reheated for a second or subsequent application. Most recycling technology has been targeted at taking the rubber and treating it in a manner to allow it to "cross-link" or bond with other virgin or recycled material. Laboratory and engineering experiments have shown that surface treating of crumb rubber particles (20 mesh or smaller) does produce a surface condition that does cross-link. Two of the surface treatment methods are special polymers and the use of reactive gas. Untreated rubber/fiber is being used in a number of applications where it is not surface treated. One application of rubber and fiber particles is the "Tire Turf" for running tracks and athletic fields. Untreated crumb rubber has been used in asphalt rubber for roads but in small quantities and has the disadvantage of being considerably more costly than standard asphalt. Some of the recycling research has included the blending of recycled treated rubber particles with thermoplastic materials and has proven successful. Market development has been hindered by the high cost of separation of the tire components and the fact that potential users get into the chicken and egg dilemma. Recycled rubber users need to see a capability to produce the high production levels needed before they enter into the cost of development, engineering changes, etc. On the other hand, the developers of the raw material from scrap tires need to have some assurance that, if they develop such a capability, a customer exists.
As set forth in the paper entitled "Thermal Depolymerisation of Waste Tires by Heavy Oils. Conversion Into Fuels" presented by F. Audibert and J. P. Beaufils at the International Symposium on Scrap Tire Disposal on Oct. 21 and 22, 1982, the French Institute of Petroleum has developed a process of valorisation of waste tires into fuels. The process consisted of sprinkling tires held in a basket with a contacting oil heated to a temperature of up to 380.degree. C. However, this process was merely a pilot study, which is believed not to have resulted in any production or commercial processes as being generally not practical and too costly. Additionally, using crude oil as the contacting oil, many distillate products and volatile and/or aromatic ingredients were created, producing other concerns including environmental concerns.